In situ self-calibration of profile height measurement of interferometric microscope

The self-calibration method which detects the derivative function of the calibration curve without using any references or any additional sensors has been applied to an interferometric microscope. Two specimens were used to get the discrete derivative function of the calibration curve. One is an inclined flat surface which gives a continuous input value of the calibration. The difference between two measurements which are obtained before and after a small shift in the height direction is used for getting a derivative function of the wanted calibration curve. The other is a step specimen whose step-height determines the small displacement of the calibration curve to get discrete derivative of the function. The results by these two methods have shown good agreement with each other to confirm the effectiveness and reliability of the proposed method. With the calibration and the correction, the variation of small step-height measurement is reduced to 0.5% which is 1/4 of the original one.